The browser solves the problem of not having any open API. Each platform wants to handle things in its own way, and the browser is the perfect way to do that. Each service, including both the open and the proprietary ones, can present the feed in the way that they decide is right. The browser already does handle rudimentary account management via form auto fill, as well as a unified notification system.
But as for a unified feed… I think the best example is the issues with that come from Lemmy/Mastodon integration. Mastodon posts have a different mentality than Lemmy posts do, not to mention with structure of responses. I just don’t think it does us any favors to have them share the same feed. Now we have replies that have a clear structure of who they are responding to, but Mastodon users come in adding the user tag into the comment, which is messy at best, and bordering obnoxious at worst.
But I get it, I’m not the audience you’re looking to cater to. I don’t particularly understand the value of RSS readers at all, because I just go directly to the services I want to see the feeds from. Hell, I don’t even use bookmarks. I type in the web address for my services every time